1. Field of the Invention
The present invention relates to a magnetic recording medium used for perpendicular magnetic recording and a magnetic recording and reproducing apparatus.
2. Description of the Related Art
Perpendicular magnetic recording which enables high recording density by longitudinal recording has attracted attention in the field of magnetic recording. A single layer medium 71 shown in FIG. 8A and a double-layer medium 74 shown in FIG. 8B are known as a magnetic recording medium used for perpendicular magnetic recording.
A single layer medium 71 is formed by laminating a perpendicular magnetic recording layer 73 on a non-magnetic substrate 72. A double-layer medium 74 is formed by laminating a soft magnetic layer 76 and a perpendicular magnetic recording layer 77 in that order on a non-magnetic substrate 75. A protective layer and a lubricant layer (both of them are not shown) are formed on the perpendicular magnetic recording layer in both of cases of the single layer medium and the double-layer medium.
A reproducing head 78 is a shielded type magnetoresistance effect element head. A pair of shielding layers 79a, 79b are provided so as to sandwich a non-magnetic layer 81 and a magnetoresistance effect element 80 is disposed at a part of the non-magnetic layer 81 between the shielding layers 79a and 79b. 
A recording head is not shown. Nevertheless, as a magnetic field component (perpendicular component) in a thickness direction of the perpendicular magnetic recording layers 73 and 77 is required, a head having a main magnetic pole to obtain larger perpendicular component of recording magnetic field is used instead of a ring type recording head used in an longitudinal recording medium.
The single layer medium and the double-layer medium respectively have advantages and disadvantages for recording and reproducing.
The double-layer medium is superior to the single layer medium for recording in a magnetic recording medium for perpendicular magnetic recording. The reason is as follows. Namely, in accordance with the double-layer medium, as a result of soft magnetic layer taking in lines of magnetic force from a main magnetic pole in unillustrated recording head, the lines of magnetic force from the main magnetic pole act on the perpendicular magnetic recording layer with larger perpendicular component. That is to say, the soft magnetic layer amplifies the perpendicular component of recording magnetic field in the perpendicular magnetic recording layer.
Nevertheless, the single layer medium is superior to the double-layer medium for reproducing the magnetic recording medium for perpendicular magnetic recording. In accordance with the double-layer medium, because the soft magnetic layer is provided, a signal magnetic field loop from a recording magnetization of perpendicular magnetic recording layer is extended, so that a resolution of reproduction is decreased.
The signal magnetic field loop from recording magnetization of the perpendicular magnetic recording layer is large in a case of the double-layer medium with the soft magnetic layer and is small in a case of the single layer medium without the soft magnetic layer. This is because the soft magnetic layer extends the signal magnetic field loop. Extension of the signal magnetic field loop decreases a resolution of reproduction. In order to increase the resolution of reproduction, it is ideal to pick up only the signal magnetic field loop from the recording magnetization immediately below the magnetoresistance effect element 80.
In a case of the single layer medium 71, as shown in FIG. 9A, a signal magnetic field loop 92 from a recording magnetization 91 which is apart from an area immediately below the magnetoresistance effect element 80 is not so extended. This is because the soft magnetic layer is not provided. The signal magnetic field loop 92 enters the shielding layer 79a and circulates to the recording magnetization 91 without passing through the magnetoresistance effect element 80. That is to say, the magnetoresistance effect element 80 does not pick up the signal magnetic field loop from the recording magnetization 91 placed apart from an area immediately below the magnetoresistance effect element 80. The resolution of reproduction is high from this standpoint.
On the other hand, in a case of the double-layer medium 74, as shown in FIG. 9B, a signal magnetic field loop 94 from a recording magnetization 93 of perpendicular magnetic recording layer 77 is extended because of soft magnetic layer 76. The signal magnetic field loop circulates via the shielding layer 79a, the magnetoresistance effect element 80, the perpendicular magnetic recording layer 77 and the soft magnetic layer 76 to the recording magnetization 93. As a result of the signal magnetic field loop 94 being extended, the signal magnetic field loop 94 from the recording magnetization 93 at an area spaced apart from an area immediately below the magnetoresistance effect element 80 is picked up by the magnetoresistance effect element 80. This leads to a decrease in the resolution of reproduction.
FIG. 10 shows linear recording density dependency of reproduced output. With respect to a unit of linear recording density, i.e., xe2x80x9ckFCIxe2x80x9d, xe2x80x9ckxe2x80x9d indicates 103 and xe2x80x9cFCIxe2x80x9d indicates Flux Change per Inch. A reproduced output obtained when the linear recording density is 100 kFCI in the double-layer medium is standardized as xe2x80x9c1xe2x80x9d. A characteristic curve of the double-layer medium has large rate of change and a characteristic curve of the single layer medium has small rate of change. Larger reproduced output is preferable but in order to improve the resolution of reproduction, it is preferable that not the reproduced output but a rate of change is smaller. An output halving recording density D50 which is a representative example of linear recording density resolution indicates a linear recording density at 50% of peak value of reproduced output. The output halving recording density D50 of the double-layer medium is 510 kFCI (which is a value corresponding to 0.5, i.e., a half of peak value 1). In contrast, the output halving recording density D50 of the single layer medium is 630 kFCI (which is a value corresponding to 0.27, i.e., a half of peak value 0.54). The output halving recording density D50 of the single layer medium is larger than that of the double-layer medium. A resolution of reproduction of the single layer medium is superior to that of the double-layer medium.
With respect to a bit of recording magnetization in the perpendicular magnetic recording layer, upward or downward unit recording magnetization is determined as one bit (the shortest bit). As the number of unit recording magnetizations continued in the same direction is increased, long bit length is provided. On the other hand, the number of unit recording magnetizations is decreased, short bit length is provided. Namely, the larger the linear recording density is, the shorter the bit length is.
An influence of magnetic saturation of the magnetoresistance effect element is small in a case of the single layer medium because the signal magnetic field loop is small. In a case of the double-layer medium, the influence is exhibited because the signal magnetic field loop is extended. Still, in a case of shorter bit length, signal magnetic field loops reaching the magnetoresistance effect element 80 are alternately orientated and offset each other, so that the influence is not exhibited. In a case of longer bit length, signal magnetic field loops reaching the magnetoresistance effect element 80 are oriented in the same direction, so that the magnetoresistance effect element is easily saturated. This is shown in FIG. 10. Namely, closer to longer bit length side, i.e., lower linear recording density side, the reproduced output becomes significantly larger in the double-layer medium. If saturation occurs, a reproduced signal is deteriorated. Magnetic saturation occurs at a yoke type reproducing head more remarkably than a shielded type reproducing head.
As described above, in accordance with the single layer medium, a resolution of reproduction is excellent because a soft magnetic layer is not provided but recording characteristic is inferior. On the other hand, in accordance with the double-layer medium, the recording characteristic is excellent because of the soft magnetic layer but the resolution of reproduction is decreased because of the soft magnetic layer provided to improve the recording characteristic. The soft magnetic layer improves the recording characteristic but at the same time causes a decrease in the resolution of reproduction.
FIG. 11 show a yoke type reproducing head. FIG. 11A shows a case of the single layer medium 71 and FIG. 11B shows a case of the double-layer medium 74. A reference numeral 61 denotes a reproducing head, a reference numeral 62 denotes a gap layer, a reference numeral 63 denotes a first yoke, a reference numeral 64 denotes a second yoke, a reference numeral 64a denotes a front yoke, a reference numeral 64b denotes a back yoke and a reference numeral 65 denotes a magnetoresistance effect element.
In a case of the single layer medium 71, as shown in FIG. 11A, a signal magnetic field loop 92 generated from a recording magnetization 91 enters the first yoke 63 and does not reach the gap layer 62. Thus, the signal magnetic field loop does not enter the magnetoresistance effect element 65.
In a case of the double-layer medium 74, however, as shown in FIG. 11B, as the soft magnetic layer 76 is formed, a magnetic resistance is decreased. A signal magnetic field loop 94 generated from a recording magnetization 93 extends via the gap layer 62 to the first yoke 63 and the front yoke 64a. A part of the signal magnetic field loop circulates within a magnetic circuit of the reproducing head 61, enters the magnetoresistance effect element 65 and is reproduced. That is to say, as a signal of the recording magnetization 93 which is not placed immediately below the gap layer 62 is reproduced, a resolution of reproduction is decreased. Further, at a time of reproducing a signal with longer bit length, totally large signal magnetic field loop enters the reproducing head 61, so that the magnetoresistance effect element 65 is saturated. As a result, a signal cannot be properly reproduced.
Accordingly, a major object of the present invention is to solve the above-described drawbacks and to provide a magnetic recording medium and a magnetic recording and reproducing apparatus that sufficient recording magnetic field can be obtained at a time of recording and excellent resolution can be obtained at a time of reproduction.
Other objects, characteristics and advantages of the present invention will be apparent from the following description.
In order to accomplish the aforementioned object, the present invention provides the following sections in a magnetic recording medium for perpendicular magnetic recording. A soft magnetic layer is formed on a non-magnetic substrate. The soft magnetic layer is used to increase a perpendicular component of recording magnetic field in a perpendicular magnetic recording layer to be described later. A non-magnetic layer is formed on the soft magnetic layer. Then, a perpendicular magnetic recording layer is formed on the non-magnetic layer. The non-magnetic layer interposed between the soft magnetic layer and the perpendicular magnetic recording layer acts so as to suppress extension of signal magnetic field loop from recording magnetization in the perpendicular magnetic recording layer. That is to say, the non-magnetic layer is used to reduce the signal magnetic field loop from the recording magnetization. The non-magnetic layer has a thickness required to effectively reduce the signal magnetic field loop. The required thickness desirably exceeds 20 nm. The thickness of the non-magnetic layer is preferably larger in view of reducing the signal magnetic field loop generated from the recording magnetization in the perpendicular magnetic recording layer. An actual upper limit of the thickness is determined in order to control a total thickness of magnetic recording medium.
In summary, a magnetic recording medium of the present invention comprises a non-magnetic substrate, a soft magnetic layer formed on the substrate, a non-magnetic layer formed on the soft magnetic layer, and a perpendicular magnetic recording layer formed on the non-magnetic layer. The non-magnetic layer has a thickness required to reduce a signal magnetic field loop of recording magnetization of the perpendicular magnetic recording layer.
An operation of such structure is as follows. Namely, at a time of recording, sufficiently large perpendicular component of the recording magnetic field can be obtained because of the soft magnetic layer. At a time of reproduction, a magnetic resistance between the perpendicular magnetic recording layer and the soft magnetic layer is increased by the non-magnetic layer interposed between the perpendicular magnetic recording layer and the soft magnetic layer. Thus, extension of signal magnetic field loop generated from the recording magnetization in the perpendicular magnetic recording layer can be suppressed and a resolution at a time of reproduction can be improved. Further, because of the same reason, saturation of magnetoresistance effect element of reproducing head can be suppressed and thus superior reproduction characteristic can be obtained.
A method has been conventionally known in which in a double-layer medium, an intermediate layer (background layer) for improving orientation is formed on a soft magnetic layer to improve an orientation characteristic of the perpendicular magnetic recording layer, and the perpendicular magnetic recording layer is fromed on the intermediate layer. Although the intermediate layer for orientation improvement is non-magnetic, it merely acts so as to improve the orientation characteristic of the perpendicular magnetic recording layer. Namely, the intermediate layer is not used to suppress extension of signal magnetic field loop by increasing a magnetic resistance at a time of reproducing a recording magnetization subjected to perpendicular magnetic recording. The intermediate layer for orientation improvement has a thickness of a few nm or more to 20 nm or less and is desirably thin. This is not based on an idea that a loop of line of magnetic force is reduced.
In accordance with the present invention, a thickness of the non-magnetic layer between the soft magnetic layer and the perpendicular magnetic recording layer preferably exceeds 20 nm. Because of this thickness, it is possible to effectively suppress extension of signal magnetic field loop due to the soft magnetic layer. By setting such thickness, a resolution at a time of reproduction can be effectively improved.
In order to accomplish the aforementioned object, a magnetic recording and reproducing apparatus of the present invention is configured so as to record/reproduce a magnetic recording medium with a non-magnetic layer for increasing the above-described magnetic resistance being interposed between a perpendicular magnetic recording layer and a soft magnetic layer. Namely, the magnetic recording medium comprises at least a soft magnetic layer and a perpendicular magnetic recording layer on a non-magnetic substrate. Further, a non-magnetic layer is interposed between the soft magnetic layer and the perpendicular magnetic recording layer in order to increase the magnetic resistance between the perpendicular magnetic recording layer and the soft magnetic layer. The non-magnetic layer has a thickness required to reduce a signal magnetic field loop from recording magnetization of the perpendicular magnetic recording layer. The required thickness desirably exceeds 20 nm. The magnetic recording and reproducing apparatus of the present invention is configured so as to record/reproduce such magnetic recording medium.
In accordance with the magnetic recording and reproducing apparatus, because of the same reason as above described one, sufficient perpendicular component of recording magnetic field can be obtained and excellent recording characteristic can be exhibited. Further, a resolution at a time of reproduction can be made excellent, which has conventionally been considered to be difficult.
In accordance with a preferred aspect of the above magnetic recording and reproducing apparatus, a reproducing head for reproducing a magnetic recording medium with non-magnetic layer for increasing a magnetic resistance is configured as a shielded type reproducing head which has a magnetoresistance effect element which is sandwiched by shielding layers with a non-magnetic layer (which is different from the non-magnetic layer of the magnetic recording medium) being interposed therebetween. At a time of reproduction, an effect of suppressing extension of the signal magnetic field loop by the shields is exhibited and a resolution at a time of reproduction is advantageously improved.
In accordance with another preferred aspect, the reproducing head for reproducing a magnetic recording medium with non-magnetic layer for increasing a magnetic resistance is configured as a yoke type reproducing head that a magnetoresistance effect element is disposed at a part of magnetic circuit including a gap layer. In accordance with such aspect, at a time of reproduction, it is possible to prevent a signal magnetic field loop from recording magnetization of area spaced apart from an area immediately below a magnetoresistance effect element from crossing the gap layer, as well as a resolution can be improved, saturation of the magnetoresistance effect element can be suppressed and thus superior reproduction characteristic can be obtained.
A magnetic recording and reproducing apparatus in which the above-described magnetic recording medium is built may be used. Alternatively, a magnetic recording and reproducing apparatus with such magnetic recording medium being removable may be used.
A giant magnetoresistance effect element or a tunnel type magnetoresistance effect element is preferable as the magnetoresistance effect element. The giant magnetoresistance effect element is formed by laminating, at least, a magnetization fixing layer, a conductor layer and a magnetization free layer. The tunnel type magnetoresistance effect element is formed by laminating, at least, a magnetization fixing layer, an insulating layer and a magnetization free layer. In both cases, a rate of change of magnetic resistance relative to displacement of angle of rotation of magnetization is sufficiently high.